Various types of flow sensors are known in order to determine the through-flow in pipe conduits, for example heating systems. Thus, from U.S. Pat. No. 4,475,409 there is known a vortex flow measurement device. This sensor comprises an obstruction projecting into the flow, which in each case comprises a membrane on sides opposite to one another and extending parallel to the flow. In the inside of the obstruction between the membranes there is arranged a piezoelectric rod as a pressure measurement element which is deflected in dependence on the pressure difference between both membranes in order to detect the differential pressure. With the knowledge of the shape of the obstruction one may determine the flow speed on account of this differential pressure.
This known arrangement has the disadvantage that the construction of the obstruction with the inner-lying pressure measurement element is very expensive. Thus the individual membranes need to be inserted one after the another and subsequently the piezosensitive rod needs to be arranged between the membranes. Furthermore the sensor demands a relatively large construction space to the extent that it may not be applied everywhere.